If you are able to open the sound file through the source (ctrl+U or right click), you can right click on the seek bar and select "save video as..." and it will save as an mp3. Renaming the file is probably a good idea since each saved name is "sound".

Of course, this requires you to go through the levels and acquire each soundtrack one by one, which is very time consuming, and probably not the greatest quality sound you'll get. BUT it's a way to get it if nothing else!